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                    示例: Bit数组
            
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                    接口
            
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                    接口是合约
            
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                    接口类型
            
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                    实现接口的条件
            
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                    接口值
            
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                    sort.Interface接口
            
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                    http.Handler接口
            
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                    error接口
            
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                    示例: 表达式求值
            
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                    类型断言
            
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                    基于类型断言识别错误类型
            
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                    通过类型断言查询接口
            
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                    类型分支
            
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                    示例: 基于标记的XML解码
            
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                    补充几点
            
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                    Goroutines和Channels
            
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                    Goroutines
            
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                    示例: 并发的Clock服务
            
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                    示例: 并发的Echo服务
            
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                    Channels
            
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                    并发的循环
            
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                    示例: 并发的Web爬虫
            
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                    基于select的多路复用
            
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                    示例: 并发的目录遍历
            
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                    并发的退出
            
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                    示例: 聊天服务
            
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                    基于共享变量的并发
            
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                    竞争条件
            
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                    sync.Mutex互斥锁
            
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                    sync.RWMutex读写锁
            
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                    内存同步
            
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                    sync.Once惰性初始化
            
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                    竞争条件检测
            
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                    示例: 并发的非阻塞缓存
            
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                    Goroutines和线程
            
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                    包和工具
            
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                    包简介
            
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                    包声明
            
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                    包的匿名导入
            
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                    包和命名
            
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                    工具
            
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                    测试
            
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                    go test
            
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        <li class="chapter " data-level="1.12.2" data-path="../ch11/ch11-02.html">
            
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                    测试函数
            
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                    测试覆盖率
            
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                    基准测试
            
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                    剖析
            
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                    示例函数
            
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                    反射
            
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            <ul class="articles">
                
    
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                    为何需要反射?
            
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        <li class="chapter " data-level="1.13.2" data-path="../ch12/ch12-02.html">
            
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                    reflect.Type和reflect.Value
            
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        <li class="chapter " data-level="1.13.3" data-path="../ch12/ch12-03.html">
            
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                    Display递归打印
            
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        <li class="chapter " data-level="1.13.4" data-path="../ch12/ch12-04.html">
            
                <a href="../ch12/ch12-04.html">
            
                    
                    示例: 编码S表达式
            
                </a>
            

            
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        <li class="chapter " data-level="1.13.5" data-path="../ch12/ch12-05.html">
            
                <a href="../ch12/ch12-05.html">
            
                    
                    通过reflect.Value修改值
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.6" data-path="../ch12/ch12-06.html">
            
                <a href="../ch12/ch12-06.html">
            
                    
                    示例: 解码S表达式
            
                </a>
            

            
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        <li class="chapter " data-level="1.13.7" data-path="../ch12/ch12-07.html">
            
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                    获取结构体字段标签
            
                </a>
            

            
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        <li class="chapter " data-level="1.13.8" data-path="../ch12/ch12-08.html">
            
                <a href="../ch12/ch12-08.html">
            
                    
                    显示一个类型的方法集
            
                </a>
            

            
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        <li class="chapter " data-level="1.13.9" data-path="../ch12/ch12-09.html">
            
                <a href="../ch12/ch12-09.html">
            
                    
                    几点忠告
            
                </a>
            

            
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            </ul>
            
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        <li class="chapter " data-level="1.14" data-path="../ch13/ch13.html">
            
                <a href="../ch13/ch13.html">
            
                    
                    底层编程
            
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            <ul class="articles">
                
    
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                    unsafe.Sizeof, Alignof 和 Offsetof
            
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        <li class="chapter " data-level="1.14.2" data-path="../ch13/ch13-02.html">
            
                <a href="../ch13/ch13-02.html">
            
                    
                    unsafe.Pointer
            
                </a>
            

            
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        <li class="chapter " data-level="1.14.3" data-path="../ch13/ch13-03.html">
            
                <a href="../ch13/ch13-03.html">
            
                    
                    示例: 深度相等判断
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.14.4" data-path="../ch13/ch13-04.html">
            
                <a href="../ch13/ch13-04.html">
            
                    
                    通过cgo调用C代码
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.14.5" data-path="../ch13/ch13-05.html">
            
                <a href="../ch13/ch13-05.html">
            
                    
                    几点忠告
            
                </a>
            

            
        </li>
    

            </ul>
            
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        <li class="chapter " data-level="1.15" data-path="../appendix/appendix.html">
            
                <a href="../appendix/appendix.html">
            
                    
                    附录
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.15.1" data-path="../appendix/appendix-a-errata.html">
            
                <a href="../appendix/appendix-a-errata.html">
            
                    
                    附录A：原文勘误
            
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        <li class="chapter " data-level="1.15.2" data-path="../appendix/appendix-b-author.html">
            
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                    附录B：作者译者
            
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        <li class="chapter " data-level="1.15.3" data-path="../appendix/appendix-c-cpoyright.html">
            
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                    附录C：译文授权
            
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        <li class="chapter " data-level="1.15.4" data-path="../appendix/appendix-d-translations.html">
            
                <a href="../appendix/appendix-d-translations.html">
            
                    
                    附录D：其它语言
            
                </a>
            

            
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                                <h2 id="97-&#x793A;&#x4F8B;-&#x5E76;&#x53D1;&#x7684;&#x975E;&#x963B;&#x585E;&#x7F13;&#x5B58;">9.7. &#x793A;&#x4F8B;: &#x5E76;&#x53D1;&#x7684;&#x975E;&#x963B;&#x585E;&#x7F13;&#x5B58;</h2>
<p>&#x672C;&#x8282;&#x4E2D;&#x6211;&#x4EEC;&#x4F1A;&#x505A;&#x4E00;&#x4E2A;&#x65E0;&#x963B;&#x585E;&#x7684;&#x7F13;&#x5B58;&#xFF0C;&#x8FD9;&#x79CD;&#x5DE5;&#x5177;&#x53EF;&#x4EE5;&#x5E2E;&#x52A9;&#x6211;&#x4EEC;&#x6765;&#x89E3;&#x51B3;&#x73B0;&#x5B9E;&#x4E16;&#x754C;&#x4E2D;&#x5E76;&#x53D1;&#x7A0B;&#x5E8F;&#x51FA;&#x73B0;&#x4F46;&#x6CA1;&#x6709;&#x73B0;&#x6210;&#x7684;&#x5E93;&#x53EF;&#x4EE5;&#x89E3;&#x51B3;&#x7684;&#x95EE;&#x9898;&#x3002;&#x8FD9;&#x4E2A;&#x95EE;&#x9898;&#x53EB;&#x4F5C;&#x7F13;&#x5B58;&#xFF08;memoizing&#xFF09;&#x51FD;&#x6570;&#xFF08;&#x8BD1;&#x6CE8;&#xFF1A;Memoization&#x7684;&#x5B9A;&#x4E49;&#xFF1A; memoization &#x4E00;&#x8BCD;&#x662F;Donald Michie &#x6839;&#x636E;&#x62C9;&#x4E01;&#x8BED;memorandum&#x675C;&#x64B0;&#x7684;&#x4E00;&#x4E2A;&#x8BCD;&#x3002;&#x76F8;&#x5E94;&#x7684;&#x52A8;&#x8BCD;&#x3001;&#x8FC7;&#x53BB;&#x5206;&#x8BCD;&#x3001;ing&#x5F62;&#x5F0F;&#x6709;memoiz&#x3001;memoized&#x3001;memoizing&#xFF09;&#xFF0C;&#x4E5F;&#x5C31;&#x662F;&#x8BF4;&#xFF0C;&#x6211;&#x4EEC;&#x9700;&#x8981;&#x7F13;&#x5B58;&#x51FD;&#x6570;&#x7684;&#x8FD4;&#x56DE;&#x7ED3;&#x679C;&#xFF0C;&#x8FD9;&#x6837;&#x5728;&#x5BF9;&#x51FD;&#x6570;&#x8FDB;&#x884C;&#x8C03;&#x7528;&#x7684;&#x65F6;&#x5019;&#xFF0C;&#x6211;&#x4EEC;&#x5C31;&#x53EA;&#x9700;&#x8981;&#x4E00;&#x6B21;&#x8BA1;&#x7B97;&#xFF0C;&#x4E4B;&#x540E;&#x53EA;&#x8981;&#x8FD4;&#x56DE;&#x8BA1;&#x7B97;&#x7684;&#x7ED3;&#x679C;&#x5C31;&#x53EF;&#x4EE5;&#x4E86;&#x3002;&#x6211;&#x4EEC;&#x7684;&#x89E3;&#x51B3;&#x65B9;&#x6848;&#x4F1A;&#x662F;&#x5E76;&#x53D1;&#x5B89;&#x5168;&#x4E14;&#x4F1A;&#x907F;&#x514D;&#x5BF9;&#x6574;&#x4E2A;&#x7F13;&#x5B58;&#x52A0;&#x9501;&#x800C;&#x5BFC;&#x81F4;&#x6240;&#x6709;&#x64CD;&#x4F5C;&#x90FD;&#x53BB;&#x4E89;&#x4E00;&#x4E2A;&#x9501;&#x7684;&#x8BBE;&#x8BA1;&#x3002;</p>
<p>&#x6211;&#x4EEC;&#x5C06;&#x4F7F;&#x7528;&#x4E0B;&#x9762;&#x7684;httpGetBody&#x51FD;&#x6570;&#x4F5C;&#x4E3A;&#x6211;&#x4EEC;&#x9700;&#x8981;&#x7F13;&#x5B58;&#x7684;&#x51FD;&#x6570;&#x7684;&#x4E00;&#x4E2A;&#x6837;&#x4F8B;&#x3002;&#x8FD9;&#x4E2A;&#x51FD;&#x6570;&#x4F1A;&#x53BB;&#x8FDB;&#x884C;HTTP GET&#x8BF7;&#x6C42;&#x5E76;&#x4E14;&#x83B7;&#x53D6;http&#x54CD;&#x5E94;body&#x3002;&#x5BF9;&#x8FD9;&#x4E2A;&#x51FD;&#x6570;&#x7684;&#x8C03;&#x7528;&#x672C;&#x8EAB;&#x5F00;&#x9500;&#x662F;&#x6BD4;&#x8F83;&#x5927;&#x7684;&#xFF0C;&#x6240;&#x4EE5;&#x6211;&#x4EEC;&#x5C3D;&#x91CF;&#x907F;&#x514D;&#x5728;&#x4E0D;&#x5FC5;&#x8981;&#x7684;&#x65F6;&#x5019;&#x53CD;&#x590D;&#x8C03;&#x7528;&#x3002;</p>
<pre><code class="lang-go"><span class="hljs-keyword">func</span> httpGetBody(url <span class="hljs-keyword">string</span>) (<span class="hljs-keyword">interface</span>{}, error) {
    resp, err := http.Get(url)
    <span class="hljs-keyword">if</span> err != <span class="hljs-literal">nil</span> {
        <span class="hljs-keyword">return</span> <span class="hljs-literal">nil</span>, err
    }
    <span class="hljs-keyword">defer</span> resp.Body.Close()
    <span class="hljs-keyword">return</span> ioutil.ReadAll(resp.Body)
}
</code></pre>
<p>&#x6700;&#x540E;&#x4E00;&#x884C;&#x7A0D;&#x5FAE;&#x9690;&#x85CF;&#x4E86;&#x4E00;&#x4E9B;&#x7EC6;&#x8282;&#x3002;ReadAll&#x4F1A;&#x8FD4;&#x56DE;&#x4E24;&#x4E2A;&#x7ED3;&#x679C;&#xFF0C;&#x4E00;&#x4E2A;[]byte&#x6570;&#x7EC4;&#x548C;&#x4E00;&#x4E2A;&#x9519;&#x8BEF;&#xFF0C;&#x4E0D;&#x8FC7;&#x8FD9;&#x4E24;&#x4E2A;&#x5BF9;&#x8C61;&#x53EF;&#x4EE5;&#x88AB;&#x8D4B;&#x503C;&#x7ED9;httpGetBody&#x7684;&#x8FD4;&#x56DE;&#x58F0;&#x660E;&#x91CC;&#x7684;interface{}&#x548C;error&#x7C7B;&#x578B;&#xFF0C;&#x6240;&#x4EE5;&#x6211;&#x4EEC;&#x4E5F;&#x5C31;&#x53EF;&#x4EE5;&#x8FD9;&#x6837;&#x8FD4;&#x56DE;&#x7ED3;&#x679C;&#x5E76;&#x4E14;&#x4E0D;&#x9700;&#x8981;&#x989D;&#x5916;&#x7684;&#x5DE5;&#x4F5C;&#x4E86;&#x3002;&#x6211;&#x4EEC;&#x5728;httpGetBody&#x4E2D;&#x9009;&#x7528;&#x8FD9;&#x79CD;&#x8FD4;&#x56DE;&#x7C7B;&#x578B;&#x662F;&#x4E3A;&#x4E86;&#x4F7F;&#x5176;&#x53EF;&#x4EE5;&#x4E0E;&#x7F13;&#x5B58;&#x5339;&#x914D;&#x3002;</p>
<p>&#x4E0B;&#x9762;&#x662F;&#x6211;&#x4EEC;&#x8981;&#x8BBE;&#x8BA1;&#x7684;cache&#x7684;&#x7B2C;&#x4E00;&#x4E2A;&#x201C;&#x8349;&#x7A3F;&#x201D;&#xFF1A;</p>
<p><u><i>gopl.io/ch9/memo1</i></u></p>
<pre><code class="lang-go"><span class="hljs-comment">// Package memo provides a concurrency-unsafe</span>
<span class="hljs-comment">// memoization of a function of type Func.</span>
<span class="hljs-keyword">package</span> memo

<span class="hljs-comment">// A Memo caches the results of calling a Func.</span>
<span class="hljs-keyword">type</span> Memo <span class="hljs-keyword">struct</span> {
    f     Func
    cache <span class="hljs-keyword">map</span>[<span class="hljs-keyword">string</span>]result
}

<span class="hljs-comment">// Func is the type of the function to memoize.</span>
<span class="hljs-keyword">type</span> Func <span class="hljs-keyword">func</span>(key <span class="hljs-keyword">string</span>) (<span class="hljs-keyword">interface</span>{}, error)

<span class="hljs-keyword">type</span> result <span class="hljs-keyword">struct</span> {
    value <span class="hljs-keyword">interface</span>{}
    err   error
}

<span class="hljs-keyword">func</span> New(f Func) *Memo {
    <span class="hljs-keyword">return</span> &amp;Memo{f: f, cache: <span class="hljs-built_in">make</span>(<span class="hljs-keyword">map</span>[<span class="hljs-keyword">string</span>]result)}
}

<span class="hljs-comment">// <span class="hljs-doctag">NOTE:</span> not concurrency-safe!</span>
<span class="hljs-keyword">func</span> (memo *Memo) Get(key <span class="hljs-keyword">string</span>) (<span class="hljs-keyword">interface</span>{}, error) {
    res, ok := memo.cache[key]
    <span class="hljs-keyword">if</span> !ok {
        res.value, res.err = memo.f(key)
        memo.cache[key] = res
    }
    <span class="hljs-keyword">return</span> res.value, res.err
}
</code></pre>
<p>Memo&#x5B9E;&#x4F8B;&#x4F1A;&#x8BB0;&#x5F55;&#x9700;&#x8981;&#x7F13;&#x5B58;&#x7684;&#x51FD;&#x6570;f&#xFF08;&#x7C7B;&#x578B;&#x4E3A;Func&#xFF09;&#xFF0C;&#x4EE5;&#x53CA;&#x7F13;&#x5B58;&#x5185;&#x5BB9;&#xFF08;&#x91CC;&#x9762;&#x662F;&#x4E00;&#x4E2A;string&#x5230;result&#x6620;&#x5C04;&#x7684;map&#xFF09;&#x3002;&#x6BCF;&#x4E00;&#x4E2A;result&#x90FD;&#x662F;&#x7B80;&#x5355;&#x7684;&#x51FD;&#x6570;&#x8FD4;&#x56DE;&#x7684;&#x503C;&#x5BF9;&#x513F;&#x2014;&#x2014;&#x4E00;&#x4E2A;&#x503C;&#x548C;&#x4E00;&#x4E2A;&#x9519;&#x8BEF;&#x503C;&#x3002;&#x7EE7;&#x7EED;&#x4E0B;&#x53BB;&#x6211;&#x4EEC;&#x4F1A;&#x5C55;&#x793A;&#x4E00;&#x4E9B;Memo&#x7684;&#x53D8;&#x79CD;&#xFF0C;&#x4E0D;&#x8FC7;&#x6240;&#x6709;&#x7684;&#x4F8B;&#x5B50;&#x90FD;&#x4F1A;&#x9075;&#x5FAA;&#x4E0A;&#x9762;&#x7684;&#x8FD9;&#x4E9B;&#x65B9;&#x9762;&#x3002;</p>
<p>&#x4E0B;&#x9762;&#x662F;&#x4E00;&#x4E2A;&#x4F7F;&#x7528;Memo&#x7684;&#x4F8B;&#x5B50;&#x3002;&#x5BF9;&#x4E8E;&#x6D41;&#x5165;&#x7684;URL&#x7684;&#x6BCF;&#x4E00;&#x4E2A;&#x5143;&#x7D20;&#x6211;&#x4EEC;&#x90FD;&#x4F1A;&#x8C03;&#x7528;Get&#xFF0C;&#x5E76;&#x6253;&#x5370;&#x8C03;&#x7528;&#x5EF6;&#x65F6;&#x4EE5;&#x53CA;&#x5176;&#x8FD4;&#x56DE;&#x7684;&#x6570;&#x636E;&#x5927;&#x5C0F;&#x7684;log&#xFF1A;</p>
<pre><code class="lang-go">m := memo.New(httpGetBody)
<span class="hljs-keyword">for</span> url := <span class="hljs-keyword">range</span> incomingURLs() {
    start := time.Now()
    value, err := m.Get(url)
    <span class="hljs-keyword">if</span> err != <span class="hljs-literal">nil</span> {
        log.Print(err)
    }
    fmt.Printf(<span class="hljs-string">&quot;%s, %s, %d bytes\n&quot;</span>,
    url, time.Since(start), <span class="hljs-built_in">len</span>(value.([]<span class="hljs-keyword">byte</span>)))
}
</code></pre>
<p>&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x4F7F;&#x7528;&#x6D4B;&#x8BD5;&#x5305;&#xFF08;&#x7B2C;11&#x7AE0;&#x7684;&#x4E3B;&#x9898;&#xFF09;&#x6765;&#x7CFB;&#x7EDF;&#x5730;&#x9274;&#x5B9A;&#x7F13;&#x5B58;&#x7684;&#x6548;&#x679C;&#x3002;&#x4ECE;&#x4E0B;&#x9762;&#x7684;&#x6D4B;&#x8BD5;&#x8F93;&#x51FA;&#xFF0C;&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x770B;&#x5230;URL&#x6D41;&#x5305;&#x542B;&#x4E86;&#x4E00;&#x4E9B;&#x91CD;&#x590D;&#x7684;&#x60C5;&#x51B5;&#xFF0C;&#x5C3D;&#x7BA1;&#x6211;&#x4EEC;&#x7B2C;&#x4E00;&#x6B21;&#x5BF9;&#x6BCF;&#x4E00;&#x4E2A;URL&#x7684;<code>(*Memo).Get</code>&#x7684;&#x8C03;&#x7528;&#x90FD;&#x4F1A;&#x82B1;&#x4E0A;&#x51E0;&#x767E;&#x6BEB;&#x79D2;&#xFF0C;&#x4F46;&#x7B2C;&#x4E8C;&#x6B21;&#x5C31;&#x53EA;&#x9700;&#x8981;&#x82B1;1&#x6BEB;&#x79D2;&#x5C31;&#x53EF;&#x4EE5;&#x8FD4;&#x56DE;&#x5B8C;&#x6574;&#x7684;&#x6570;&#x636E;&#x4E86;&#x3002;</p>
<pre><code>$ go test -v gopl.io/ch9/memo1
=== RUN   Test
https://golang.org, 175.026418ms, 7537 bytes
https://godoc.org, 172.686825ms, 6878 bytes
https://play.golang.org, 115.762377ms, 5767 bytes
http://gopl.io, 749.887242ms, 2856 bytes
https://golang.org, 721ns, 7537 bytes
https://godoc.org, 152ns, 6878 bytes
https://play.golang.org, 205ns, 5767 bytes
http://gopl.io, 326ns, 2856 bytes
--- PASS: Test (1.21s)
PASS
ok  gopl.io/ch9/memo1   1.257s
</code></pre><p>&#x8FD9;&#x4E2A;&#x6D4B;&#x8BD5;&#x662F;&#x987A;&#x5E8F;&#x5730;&#x53BB;&#x505A;&#x6240;&#x6709;&#x7684;&#x8C03;&#x7528;&#x7684;&#x3002;</p>
<p>&#x7531;&#x4E8E;&#x8FD9;&#x79CD;&#x5F7C;&#x6B64;&#x72EC;&#x7ACB;&#x7684;HTTP&#x8BF7;&#x6C42;&#x53EF;&#x4EE5;&#x5F88;&#x597D;&#x5730;&#x5E76;&#x53D1;&#xFF0C;&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x628A;&#x8FD9;&#x4E2A;&#x6D4B;&#x8BD5;&#x6539;&#x6210;&#x5E76;&#x53D1;&#x5F62;&#x5F0F;&#x3002;&#x53EF;&#x4EE5;&#x4F7F;&#x7528;sync.WaitGroup&#x6765;&#x7B49;&#x5F85;&#x6240;&#x6709;&#x7684;&#x8BF7;&#x6C42;&#x90FD;&#x5B8C;&#x6210;&#x4E4B;&#x540E;&#x518D;&#x8FD4;&#x56DE;&#x3002;</p>
<pre><code class="lang-go">m := memo.New(httpGetBody)
<span class="hljs-keyword">var</span> n sync.WaitGroup
<span class="hljs-keyword">for</span> url := <span class="hljs-keyword">range</span> incomingURLs() {
    n.Add(<span class="hljs-number">1</span>)
    <span class="hljs-keyword">go</span> <span class="hljs-keyword">func</span>(url <span class="hljs-keyword">string</span>) {
        start := time.Now()
        value, err := m.Get(url)
        <span class="hljs-keyword">if</span> err != <span class="hljs-literal">nil</span> {
            log.Print(err)
        }
        fmt.Printf(<span class="hljs-string">&quot;%s, %s, %d bytes\n&quot;</span>,
        url, time.Since(start), <span class="hljs-built_in">len</span>(value.([]<span class="hljs-keyword">byte</span>)))
        n.Done()
    }(url)
}
n.Wait()
</code></pre>
<p>&#x8FD9;&#x6B21;&#x6D4B;&#x8BD5;&#x8DD1;&#x8D77;&#x6765;&#x66F4;&#x5FEB;&#x4E86;&#xFF0C;&#x7136;&#x800C;&#x4E0D;&#x5E78;&#x7684;&#x662F;&#x8C8C;&#x4F3C;&#x8FD9;&#x4E2A;&#x6D4B;&#x8BD5;&#x4E0D;&#x662F;&#x6BCF;&#x6B21;&#x90FD;&#x80FD;&#x591F;&#x6B63;&#x5E38;&#x5DE5;&#x4F5C;&#x3002;&#x6211;&#x4EEC;&#x6CE8;&#x610F;&#x5230;&#x6709;&#x4E00;&#x4E9B;&#x610F;&#x6599;&#x4E4B;&#x5916;&#x7684;cache miss&#xFF08;&#x7F13;&#x5B58;&#x672A;&#x547D;&#x4E2D;&#xFF09;&#xFF0C;&#x6216;&#x8005;&#x547D;&#x4E2D;&#x4E86;&#x7F13;&#x5B58;&#x4F46;&#x5374;&#x8FD4;&#x56DE;&#x4E86;&#x9519;&#x8BEF;&#x7684;&#x503C;&#xFF0C;&#x6216;&#x8005;&#x751A;&#x81F3;&#x4F1A;&#x76F4;&#x63A5;&#x5D29;&#x6E83;&#x3002;</p>
<p>&#x4F46;&#x66F4;&#x7CDF;&#x7CD5;&#x7684;&#x662F;&#xFF0C;&#x6709;&#x65F6;&#x5019;&#x8FD9;&#x4E2A;&#x7A0B;&#x5E8F;&#x8FD8;&#x662F;&#x80FD;&#x6B63;&#x786E;&#x7684;&#x8FD0;&#x884C;&#xFF08;&#x8BD1;&#xFF1A;&#x4E5F;&#x5C31;&#x662F;&#x6700;&#x8BA9;&#x4EBA;&#x5D29;&#x6E83;&#x7684;&#x5076;&#x53D1;bug&#xFF09;&#xFF0C;&#x6240;&#x4EE5;&#x6211;&#x4EEC;&#x751A;&#x81F3;&#x53EF;&#x80FD;&#x90FD;&#x4E0D;&#x4F1A;&#x610F;&#x8BC6;&#x5230;&#x8FD9;&#x4E2A;&#x7A0B;&#x5E8F;&#x6709;bug&#x3002;&#x4F46;&#x662F;&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x4F7F;&#x7528;-race&#x8FD9;&#x4E2A;flag&#x6765;&#x8FD0;&#x884C;&#x7A0B;&#x5E8F;&#xFF0C;&#x7ADE;&#x4E89;&#x68C0;&#x6D4B;&#x5668;&#xFF08;&#xA7;9.6&#xFF09;&#x4F1A;&#x6253;&#x5370;&#x50CF;&#x4E0B;&#x9762;&#x8FD9;&#x6837;&#x7684;&#x62A5;&#x544A;&#xFF1A;</p>
<pre><code>$ go test -run=TestConcurrent -race -v gopl.io/ch9/memo1
=== RUN   TestConcurrent
...
WARNING: DATA RACE
Write by goroutine 36:
  runtime.mapassign1()
      ~/go/src/runtime/hashmap.go:411 +0x0
  gopl.io/ch9/memo1.(*Memo).Get()
      ~/gobook2/src/gopl.io/ch9/memo1/memo.go:32 +0x205
  ...
Previous write by goroutine 35:
  runtime.mapassign1()
      ~/go/src/runtime/hashmap.go:411 +0x0
  gopl.io/ch9/memo1.(*Memo).Get()
      ~/gobook2/src/gopl.io/ch9/memo1/memo.go:32 +0x205
...
Found 1 data race(s)
FAIL    gopl.io/ch9/memo1   2.393s
</code></pre><p>memo.go&#x7684;32&#x884C;&#x51FA;&#x73B0;&#x4E86;&#x4E24;&#x6B21;&#xFF0C;&#x8BF4;&#x660E;&#x6709;&#x4E24;&#x4E2A;goroutine&#x5728;&#x6CA1;&#x6709;&#x540C;&#x6B65;&#x5E72;&#x9884;&#x7684;&#x60C5;&#x51B5;&#x4E0B;&#x66F4;&#x65B0;&#x4E86;cache map&#x3002;&#x8FD9;&#x8868;&#x660E;Get&#x4E0D;&#x662F;&#x5E76;&#x53D1;&#x5B89;&#x5168;&#x7684;&#xFF0C;&#x5B58;&#x5728;&#x6570;&#x636E;&#x7ADE;&#x4E89;&#x3002;</p>
<pre><code class="lang-go"><span class="hljs-number">28</span>  <span class="hljs-keyword">func</span> (memo *Memo) Get(key <span class="hljs-keyword">string</span>) (<span class="hljs-keyword">interface</span>{}, error) {
<span class="hljs-number">29</span>      res, ok := memo.cache(key)
<span class="hljs-number">30</span>      <span class="hljs-keyword">if</span> !ok {
<span class="hljs-number">31</span>          res.value, res.err = memo.f(key)
<span class="hljs-number">32</span>          memo.cache[key] = res
<span class="hljs-number">33</span>      }
<span class="hljs-number">34</span>      <span class="hljs-keyword">return</span> res.value, res.err
<span class="hljs-number">35</span>  }
</code></pre>
<p>&#x6700;&#x7B80;&#x5355;&#x7684;&#x4F7F;cache&#x5E76;&#x53D1;&#x5B89;&#x5168;&#x7684;&#x65B9;&#x5F0F;&#x662F;&#x4F7F;&#x7528;&#x57FA;&#x4E8E;&#x76D1;&#x63A7;&#x7684;&#x540C;&#x6B65;&#x3002;&#x53EA;&#x8981;&#x7ED9;Memo&#x52A0;&#x4E0A;&#x4E00;&#x4E2A;mutex&#xFF0C;&#x5728;Get&#x7684;&#x4E00;&#x5F00;&#x59CB;&#x83B7;&#x53D6;&#x4E92;&#x65A5;&#x9501;&#xFF0C;return&#x7684;&#x65F6;&#x5019;&#x91CA;&#x653E;&#x9501;&#xFF0C;&#x5C31;&#x53EF;&#x4EE5;&#x8BA9;cache&#x7684;&#x64CD;&#x4F5C;&#x53D1;&#x751F;&#x5728;&#x4E34;&#x754C;&#x533A;&#x5185;&#x4E86;&#xFF1A;</p>
<p><u><i>gopl.io/ch9/memo2</i></u></p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> Memo <span class="hljs-keyword">struct</span> {
    f     Func
    mu    sync.Mutex <span class="hljs-comment">// guards cache</span>
    cache <span class="hljs-keyword">map</span>[<span class="hljs-keyword">string</span>]result
}

<span class="hljs-comment">// Get is concurrency-safe.</span>
<span class="hljs-keyword">func</span> (memo *Memo) Get(key <span class="hljs-keyword">string</span>) (value <span class="hljs-keyword">interface</span>{}, err error) {
    memo.mu.Lock()
    res, ok := memo.cache[key]
    <span class="hljs-keyword">if</span> !ok {
        res.value, res.err = memo.f(key)
        memo.cache[key] = res
    }
    memo.mu.Unlock()
    <span class="hljs-keyword">return</span> res.value, res.err
}
</code></pre>
<p>&#x6D4B;&#x8BD5;&#x4F9D;&#x7136;&#x5E76;&#x53D1;&#x8FDB;&#x884C;&#xFF0C;&#x4F46;&#x8FD9;&#x56DE;&#x7ADE;&#x4E89;&#x68C0;&#x67E5;&#x5668;&#x201C;&#x6C89;&#x9ED8;&#x201D;&#x4E86;&#x3002;&#x4E0D;&#x5E78;&#x7684;&#x662F;&#x5BF9;&#x4E8E;Memo&#x7684;&#x8FD9;&#x4E00;&#x70B9;&#x6539;&#x53D8;&#x4F7F;&#x6211;&#x4EEC;&#x5B8C;&#x5168;&#x4E27;&#x5931;&#x4E86;&#x5E76;&#x53D1;&#x7684;&#x6027;&#x80FD;&#x4F18;&#x70B9;&#x3002;&#x6BCF;&#x6B21;&#x5BF9;f&#x7684;&#x8C03;&#x7528;&#x671F;&#x95F4;&#x90FD;&#x4F1A;&#x6301;&#x6709;&#x9501;&#xFF0C;Get&#x5C06;&#x672C;&#x6765;&#x53EF;&#x4EE5;&#x5E76;&#x884C;&#x8FD0;&#x884C;&#x7684;I/O&#x64CD;&#x4F5C;&#x4E32;&#x884C;&#x5316;&#x4E86;&#x3002;&#x6211;&#x4EEC;&#x672C;&#x7AE0;&#x7684;&#x76EE;&#x7684;&#x662F;&#x5B8C;&#x6210;&#x4E00;&#x4E2A;&#x65E0;&#x9501;&#x7F13;&#x5B58;&#xFF0C;&#x800C;&#x4E0D;&#x662F;&#x73B0;&#x5728;&#x8FD9;&#x6837;&#x7684;&#x5C06;&#x6240;&#x6709;&#x8BF7;&#x6C42;&#x4E32;&#x884C;&#x5316;&#x7684;&#x51FD;&#x6570;&#x7684;&#x7F13;&#x5B58;&#x3002;</p>
<p>&#x4E0B;&#x4E00;&#x4E2A;Get&#x7684;&#x5B9E;&#x73B0;&#xFF0C;&#x8C03;&#x7528;Get&#x7684;goroutine&#x4F1A;&#x4E24;&#x6B21;&#x83B7;&#x53D6;&#x9501;&#xFF1A;&#x67E5;&#x627E;&#x9636;&#x6BB5;&#x83B7;&#x53D6;&#x4E00;&#x6B21;&#xFF0C;&#x5982;&#x679C;&#x67E5;&#x627E;&#x6CA1;&#x6709;&#x8FD4;&#x56DE;&#x4EFB;&#x4F55;&#x5185;&#x5BB9;&#xFF0C;&#x90A3;&#x4E48;&#x8FDB;&#x5165;&#x66F4;&#x65B0;&#x9636;&#x6BB5;&#x4F1A;&#x518D;&#x6B21;&#x83B7;&#x53D6;&#x3002;&#x5728;&#x8FD9;&#x4E24;&#x6B21;&#x83B7;&#x53D6;&#x9501;&#x7684;&#x4E2D;&#x95F4;&#x9636;&#x6BB5;&#xFF0C;&#x5176;&#x5B83;goroutine&#x53EF;&#x4EE5;&#x968F;&#x610F;&#x4F7F;&#x7528;cache&#x3002;</p>
<p><u><i>gopl.io/ch9/memo3</i></u></p>
<pre><code class="lang-go"><span class="hljs-keyword">func</span> (memo *Memo) Get(key <span class="hljs-keyword">string</span>) (value <span class="hljs-keyword">interface</span>{}, err error) {
    memo.mu.Lock()
    res, ok := memo.cache[key]
    memo.mu.Unlock()
    <span class="hljs-keyword">if</span> !ok {
        res.value, res.err = memo.f(key)

        <span class="hljs-comment">// Between the two critical sections, several goroutines</span>
        <span class="hljs-comment">// may race to compute f(key) and update the map.</span>
        memo.mu.Lock()
        memo.cache[key] = res
        memo.mu.Unlock()
    }
    <span class="hljs-keyword">return</span> res.value, res.err
}
</code></pre>
<p>&#x8FD9;&#x4E9B;&#x4FEE;&#x6539;&#x4F7F;&#x6027;&#x80FD;&#x518D;&#x6B21;&#x5F97;&#x5230;&#x4E86;&#x63D0;&#x5347;&#xFF0C;&#x4F46;&#x6709;&#x4E00;&#x4E9B;URL&#x88AB;&#x83B7;&#x53D6;&#x4E86;&#x4E24;&#x6B21;&#x3002;&#x8FD9;&#x79CD;&#x60C5;&#x51B5;&#x5728;&#x4E24;&#x4E2A;&#x4EE5;&#x4E0A;&#x7684;goroutine&#x540C;&#x4E00;&#x65F6;&#x523B;&#x8C03;&#x7528;Get&#x6765;&#x8BF7;&#x6C42;&#x540C;&#x6837;&#x7684;URL&#x65F6;&#x4F1A;&#x53D1;&#x751F;&#x3002;&#x591A;&#x4E2A;goroutine&#x4E00;&#x8D77;&#x67E5;&#x8BE2;cache&#xFF0C;&#x53D1;&#x73B0;&#x6CA1;&#x6709;&#x503C;&#xFF0C;&#x7136;&#x540E;&#x4E00;&#x8D77;&#x8C03;&#x7528;f&#x8FD9;&#x4E2A;&#x6162;&#x4E0D;&#x62C9;&#x53FD;&#x7684;&#x51FD;&#x6570;&#x3002;&#x5728;&#x5F97;&#x5230;&#x7ED3;&#x679C;&#x540E;&#xFF0C;&#x4E5F;&#x90FD;&#x4F1A;&#x53BB;&#x66F4;&#x65B0;map&#x3002;&#x5176;&#x4E2D;&#x4E00;&#x4E2A;&#x83B7;&#x5F97;&#x7684;&#x7ED3;&#x679C;&#x4F1A;&#x8986;&#x76D6;&#x6389;&#x53E6;&#x4E00;&#x4E2A;&#x7684;&#x7ED3;&#x679C;&#x3002;</p>
<p>&#x7406;&#x60F3;&#x60C5;&#x51B5;&#x4E0B;&#x662F;&#x5E94;&#x8BE5;&#x907F;&#x514D;&#x6389;&#x591A;&#x4F59;&#x7684;&#x5DE5;&#x4F5C;&#x7684;&#x3002;&#x800C;&#x8FD9;&#x79CD;&#x201C;&#x907F;&#x514D;&#x201D;&#x5DE5;&#x4F5C;&#x4E00;&#x822C;&#x88AB;&#x79F0;&#x4E3A;duplicate suppression&#xFF08;&#x91CD;&#x590D;&#x6291;&#x5236;/&#x907F;&#x514D;&#xFF09;&#x3002;&#x4E0B;&#x9762;&#x7248;&#x672C;&#x7684;Memo&#x6BCF;&#x4E00;&#x4E2A;map&#x5143;&#x7D20;&#x90FD;&#x662F;&#x6307;&#x5411;&#x4E00;&#x4E2A;&#x6761;&#x76EE;&#x7684;&#x6307;&#x9488;&#x3002;&#x6BCF;&#x4E00;&#x4E2A;&#x6761;&#x76EE;&#x5305;&#x542B;&#x5BF9;&#x51FD;&#x6570;f&#x8C03;&#x7528;&#x7ED3;&#x679C;&#x7684;&#x5185;&#x5BB9;&#x7F13;&#x5B58;&#x3002;&#x4E0E;&#x4E4B;&#x524D;&#x4E0D;&#x540C;&#x7684;&#x662F;&#x8FD9;&#x6B21;entry&#x8FD8;&#x5305;&#x542B;&#x4E86;&#x4E00;&#x4E2A;&#x53EB;ready&#x7684;channel&#x3002;&#x5728;&#x6761;&#x76EE;&#x7684;&#x7ED3;&#x679C;&#x88AB;&#x8BBE;&#x7F6E;&#x4E4B;&#x540E;&#xFF0C;&#x8FD9;&#x4E2A;channel&#x5C31;&#x4F1A;&#x88AB;&#x5173;&#x95ED;&#xFF0C;&#x4EE5;&#x5411;&#x5176;&#x5B83;goroutine&#x5E7F;&#x64AD;&#xFF08;&#xA7;8.9&#xFF09;&#x53BB;&#x8BFB;&#x53D6;&#x8BE5;&#x6761;&#x76EE;&#x5185;&#x7684;&#x7ED3;&#x679C;&#x662F;&#x5B89;&#x5168;&#x7684;&#x4E86;&#x3002;</p>
<p><u><i>gopl.io/ch9/memo4</i></u></p>
<pre><code class="lang-go"><span class="hljs-keyword">type</span> entry <span class="hljs-keyword">struct</span> {
    res   result
    ready <span class="hljs-keyword">chan</span> <span class="hljs-keyword">struct</span>{} <span class="hljs-comment">// closed when res is ready</span>
}

<span class="hljs-keyword">func</span> New(f Func) *Memo {
    <span class="hljs-keyword">return</span> &amp;Memo{f: f, cache: <span class="hljs-built_in">make</span>(<span class="hljs-keyword">map</span>[<span class="hljs-keyword">string</span>]*entry)}
}

<span class="hljs-keyword">type</span> Memo <span class="hljs-keyword">struct</span> {
    f     Func
    mu    sync.Mutex <span class="hljs-comment">// guards cache</span>
    cache <span class="hljs-keyword">map</span>[<span class="hljs-keyword">string</span>]*entry
}

<span class="hljs-keyword">func</span> (memo *Memo) Get(key <span class="hljs-keyword">string</span>) (value <span class="hljs-keyword">interface</span>{}, err error) {
    memo.mu.Lock()
    e := memo.cache[key]
    <span class="hljs-keyword">if</span> e == <span class="hljs-literal">nil</span> {
        <span class="hljs-comment">// This is the first request for this key.</span>
        <span class="hljs-comment">// This goroutine becomes responsible for computing</span>
        <span class="hljs-comment">// the value and broadcasting the ready condition.</span>
        e = &amp;entry{ready: <span class="hljs-built_in">make</span>(<span class="hljs-keyword">chan</span> <span class="hljs-keyword">struct</span>{})}
        memo.cache[key] = e
        memo.mu.Unlock()

        e.res.value, e.res.err = memo.f(key)

        <span class="hljs-built_in">close</span>(e.ready) <span class="hljs-comment">// broadcast ready condition</span>
    } <span class="hljs-keyword">else</span> {
        <span class="hljs-comment">// This is a repeat request for this key.</span>
        memo.mu.Unlock()

        &lt;-e.ready <span class="hljs-comment">// wait for ready condition</span>
    }
    <span class="hljs-keyword">return</span> e.res.value, e.res.err
}
</code></pre>
<p>&#x73B0;&#x5728;Get&#x51FD;&#x6570;&#x5305;&#x62EC;&#x4E0B;&#x9762;&#x8FD9;&#x4E9B;&#x6B65;&#x9AA4;&#x4E86;&#xFF1A;&#x83B7;&#x53D6;&#x4E92;&#x65A5;&#x9501;&#x6765;&#x4FDD;&#x62A4;&#x5171;&#x4EAB;&#x53D8;&#x91CF;cache map&#xFF0C;&#x67E5;&#x8BE2;map&#x4E2D;&#x662F;&#x5426;&#x5B58;&#x5728;&#x6307;&#x5B9A;&#x6761;&#x76EE;&#xFF0C;&#x5982;&#x679C;&#x6CA1;&#x6709;&#x627E;&#x5230;&#x90A3;&#x4E48;&#x5206;&#x914D;&#x7A7A;&#x95F4;&#x63D2;&#x5165;&#x4E00;&#x4E2A;&#x65B0;&#x6761;&#x76EE;&#xFF0C;&#x91CA;&#x653E;&#x4E92;&#x65A5;&#x9501;&#x3002;&#x5982;&#x679C;&#x5B58;&#x5728;&#x6761;&#x76EE;&#x7684;&#x8BDD;&#x4E14;&#x5176;&#x503C;&#x6CA1;&#x6709;&#x5199;&#x5165;&#x5B8C;&#x6210;&#xFF08;&#x4E5F;&#x5C31;&#x662F;&#x6709;&#x5176;&#x5B83;&#x7684;goroutine&#x5728;&#x8C03;&#x7528;f&#x8FD9;&#x4E2A;&#x6162;&#x51FD;&#x6570;&#xFF09;&#x65F6;&#xFF0C;goroutine&#x5FC5;&#x987B;&#x7B49;&#x5F85;&#x503C;ready&#x4E4B;&#x540E;&#x624D;&#x80FD;&#x8BFB;&#x5230;&#x6761;&#x76EE;&#x7684;&#x7ED3;&#x679C;&#x3002;&#x800C;&#x60F3;&#x77E5;&#x9053;&#x662F;&#x5426;ready&#x7684;&#x8BDD;&#xFF0C;&#x53EF;&#x4EE5;&#x76F4;&#x63A5;&#x4ECE;ready channel&#x4E2D;&#x8BFB;&#x53D6;&#xFF0C;&#x7531;&#x4E8E;&#x8FD9;&#x4E2A;&#x8BFB;&#x53D6;&#x64CD;&#x4F5C;&#x5728;channel&#x5173;&#x95ED;&#x4E4B;&#x524D;&#x4E00;&#x76F4;&#x662F;&#x963B;&#x585E;&#x3002;</p>
<p>&#x5982;&#x679C;&#x6CA1;&#x6709;&#x6761;&#x76EE;&#x7684;&#x8BDD;&#xFF0C;&#x9700;&#x8981;&#x5411;map&#x4E2D;&#x63D2;&#x5165;&#x4E00;&#x4E2A;&#x6CA1;&#x6709;&#x51C6;&#x5907;&#x597D;&#x7684;&#x6761;&#x76EE;&#xFF0C;&#x5F53;&#x524D;&#x6B63;&#x5728;&#x8C03;&#x7528;&#x7684;goroutine&#x5C31;&#x9700;&#x8981;&#x8D1F;&#x8D23;&#x8C03;&#x7528;&#x6162;&#x51FD;&#x6570;&#x3001;&#x66F4;&#x65B0;&#x6761;&#x76EE;&#x4EE5;&#x53CA;&#x5411;&#x5176;&#x5B83;&#x6240;&#x6709;goroutine&#x5E7F;&#x64AD;&#x6761;&#x76EE;&#x5DF2;&#x7ECF;ready&#x53EF;&#x8BFB;&#x7684;&#x6D88;&#x606F;&#x4E86;&#x3002;</p>
<p>&#x6761;&#x76EE;&#x4E2D;&#x7684;e.res.value&#x548C;e.res.err&#x53D8;&#x91CF;&#x662F;&#x5728;&#x591A;&#x4E2A;goroutine&#x4E4B;&#x95F4;&#x5171;&#x4EAB;&#x7684;&#x3002;&#x521B;&#x5EFA;&#x6761;&#x76EE;&#x7684;goroutine&#x540C;&#x65F6;&#x4E5F;&#x4F1A;&#x8BBE;&#x7F6E;&#x6761;&#x76EE;&#x7684;&#x503C;&#xFF0C;&#x5176;&#x5B83;goroutine&#x5728;&#x6536;&#x5230;&quot;ready&quot;&#x7684;&#x5E7F;&#x64AD;&#x6D88;&#x606F;&#x4E4B;&#x540E;&#x7ACB;&#x523B;&#x4F1A;&#x53BB;&#x8BFB;&#x53D6;&#x6761;&#x76EE;&#x7684;&#x503C;&#x3002;&#x5C3D;&#x7BA1;&#x4F1A;&#x88AB;&#x591A;&#x4E2A;goroutine&#x540C;&#x65F6;&#x8BBF;&#x95EE;&#xFF0C;&#x4F46;&#x5374;&#x5E76;&#x4E0D;&#x9700;&#x8981;&#x4E92;&#x65A5;&#x9501;&#x3002;ready channel&#x7684;&#x5173;&#x95ED;&#x4E00;&#x5B9A;&#x4F1A;&#x53D1;&#x751F;&#x5728;&#x5176;&#x5B83;goroutine&#x63A5;&#x6536;&#x5230;&#x5E7F;&#x64AD;&#x4E8B;&#x4EF6;&#x4E4B;&#x524D;&#xFF0C;&#x56E0;&#x6B64;&#x7B2C;&#x4E00;&#x4E2A;goroutine&#x5BF9;&#x8FD9;&#x4E9B;&#x53D8;&#x91CF;&#x7684;&#x5199;&#x64CD;&#x4F5C;&#x662F;&#x4E00;&#x5B9A;&#x53D1;&#x751F;&#x5728;&#x8FD9;&#x4E9B;&#x8BFB;&#x64CD;&#x4F5C;&#x4E4B;&#x524D;&#x7684;&#x3002;&#x4E0D;&#x4F1A;&#x53D1;&#x751F;&#x6570;&#x636E;&#x7ADE;&#x4E89;&#x3002;</p>
<p>&#x8FD9;&#x6837;&#x5E76;&#x53D1;&#x3001;&#x4E0D;&#x91CD;&#x590D;&#x3001;&#x65E0;&#x963B;&#x585E;&#x7684;cache&#x5C31;&#x5B8C;&#x6210;&#x4E86;&#x3002;</p>
<p>&#x4E0A;&#x9762;&#x8FD9;&#x6837;Memo&#x7684;&#x5B9E;&#x73B0;&#x4F7F;&#x7528;&#x4E86;&#x4E00;&#x4E2A;&#x4E92;&#x65A5;&#x91CF;&#x6765;&#x4FDD;&#x62A4;&#x591A;&#x4E2A;goroutine&#x8C03;&#x7528;Get&#x65F6;&#x7684;&#x5171;&#x4EAB;map&#x53D8;&#x91CF;&#x3002;&#x4E0D;&#x59A8;&#x628A;&#x8FD9;&#x79CD;&#x8BBE;&#x8BA1;&#x548C;&#x524D;&#x9762;&#x63D0;&#x5230;&#x7684;&#x628A;map&#x53D8;&#x91CF;&#x9650;&#x5236;&#x5728;&#x4E00;&#x4E2A;&#x5355;&#x72EC;&#x7684;monitor goroutine&#x7684;&#x65B9;&#x6848;&#x505A;&#x4E00;&#x4E9B;&#x5BF9;&#x6BD4;&#xFF0C;&#x540E;&#x8005;&#x5728;&#x8C03;&#x7528;Get&#x65F6;&#x9700;&#x8981;&#x53D1;&#x6D88;&#x606F;&#x3002;</p>
<p>Func&#x3001;result&#x548C;entry&#x7684;&#x58F0;&#x660E;&#x548C;&#x4E4B;&#x524D;&#x4FDD;&#x6301;&#x4E00;&#x81F4;&#xFF1A;</p>
<pre><code class="lang-go"><span class="hljs-comment">// Func is the type of the function to memoize.</span>
<span class="hljs-keyword">type</span> Func <span class="hljs-keyword">func</span>(key <span class="hljs-keyword">string</span>) (<span class="hljs-keyword">interface</span>{}, error)

<span class="hljs-comment">// A result is the result of calling a Func.</span>
<span class="hljs-keyword">type</span> result <span class="hljs-keyword">struct</span> {
    value <span class="hljs-keyword">interface</span>{}
    err   error
}

<span class="hljs-keyword">type</span> entry <span class="hljs-keyword">struct</span> {
    res   result
    ready <span class="hljs-keyword">chan</span> <span class="hljs-keyword">struct</span>{} <span class="hljs-comment">// closed when res is ready</span>
}
</code></pre>
<p>&#x7136;&#x800C;Memo&#x7C7B;&#x578B;&#x73B0;&#x5728;&#x5305;&#x542B;&#x4E86;&#x4E00;&#x4E2A;&#x53EB;&#x505A;requests&#x7684;channel&#xFF0C;Get&#x7684;&#x8C03;&#x7528;&#x65B9;&#x7528;&#x8FD9;&#x4E2A;channel&#x6765;&#x548C;monitor goroutine&#x6765;&#x901A;&#x4FE1;&#x3002;requests channel&#x4E2D;&#x7684;&#x5143;&#x7D20;&#x7C7B;&#x578B;&#x662F;request&#x3002;Get&#x7684;&#x8C03;&#x7528;&#x65B9;&#x4F1A;&#x628A;&#x8FD9;&#x4E2A;&#x7ED3;&#x6784;&#x4E2D;&#x7684;&#x4E24;&#x7EC4;key&#x90FD;&#x586B;&#x5145;&#x597D;&#xFF0C;&#x5B9E;&#x9645;&#x4E0A;&#x7528;&#x8FD9;&#x4E24;&#x4E2A;&#x53D8;&#x91CF;&#x6765;&#x5BF9;&#x51FD;&#x6570;&#x8FDB;&#x884C;&#x7F13;&#x5B58;&#x7684;&#x3002;&#x53E6;&#x4E00;&#x4E2A;&#x53EB;response&#x7684;channel&#x4F1A;&#x88AB;&#x62FF;&#x6765;&#x53D1;&#x9001;&#x54CD;&#x5E94;&#x7ED3;&#x679C;&#x3002;&#x8FD9;&#x4E2A;channel&#x53EA;&#x4F1A;&#x4F20;&#x56DE;&#x4E00;&#x4E2A;&#x5355;&#x72EC;&#x7684;&#x503C;&#x3002;</p>
<p><u><i>gopl.io/ch9/memo5</i></u></p>
<pre><code class="lang-go"><span class="hljs-comment">// A request is a message requesting that the Func be applied to key.</span>
<span class="hljs-keyword">type</span> request <span class="hljs-keyword">struct</span> {
    key      <span class="hljs-keyword">string</span>
    response <span class="hljs-keyword">chan</span>&lt;- result <span class="hljs-comment">// the client wants a single result</span>
}

<span class="hljs-keyword">type</span> Memo <span class="hljs-keyword">struct</span>{ requests <span class="hljs-keyword">chan</span> request }
<span class="hljs-comment">// New returns a memoization of f.  Clients must subsequently call Close.</span>
<span class="hljs-keyword">func</span> New(f Func) *Memo {
    memo := &amp;Memo{requests: <span class="hljs-built_in">make</span>(<span class="hljs-keyword">chan</span> request)}
    <span class="hljs-keyword">go</span> memo.server(f)
    <span class="hljs-keyword">return</span> memo
}

<span class="hljs-keyword">func</span> (memo *Memo) Get(key <span class="hljs-keyword">string</span>) (<span class="hljs-keyword">interface</span>{}, error) {
    response := <span class="hljs-built_in">make</span>(<span class="hljs-keyword">chan</span> result)
    memo.requests &lt;- request{key, response}
    res := &lt;-response
    <span class="hljs-keyword">return</span> res.value, res.err
}

<span class="hljs-keyword">func</span> (memo *Memo) Close() { <span class="hljs-built_in">close</span>(memo.requests) }
</code></pre>
<p>&#x4E0A;&#x9762;&#x7684;Get&#x65B9;&#x6CD5;&#xFF0C;&#x4F1A;&#x521B;&#x5EFA;&#x4E00;&#x4E2A;response channel&#xFF0C;&#x628A;&#x5B83;&#x653E;&#x8FDB;request&#x7ED3;&#x6784;&#x4E2D;&#xFF0C;&#x7136;&#x540E;&#x53D1;&#x9001;&#x7ED9;monitor goroutine&#xFF0C;&#x7136;&#x540E;&#x9A6C;&#x4E0A;&#x53C8;&#x4F1A;&#x63A5;&#x6536;&#x5B83;&#x3002;</p>
<p>cache&#x53D8;&#x91CF;&#x88AB;&#x9650;&#x5236;&#x5728;&#x4E86;monitor goroutine <code>`(*Memo).server</code>&#x4E2D;&#xFF0C;&#x4E0B;&#x9762;&#x4F1A;&#x770B;&#x5230;&#x3002;monitor&#x4F1A;&#x5728;&#x5FAA;&#x73AF;&#x4E2D;&#x4E00;&#x76F4;&#x8BFB;&#x53D6;&#x8BF7;&#x6C42;&#xFF0C;&#x76F4;&#x5230;request channel&#x88AB;Close&#x65B9;&#x6CD5;&#x5173;&#x95ED;&#x3002;&#x6BCF;&#x4E00;&#x4E2A;&#x8BF7;&#x6C42;&#x90FD;&#x4F1A;&#x53BB;&#x67E5;&#x8BE2;cache&#xFF0C;&#x5982;&#x679C;&#x6CA1;&#x6709;&#x627E;&#x5230;&#x6761;&#x76EE;&#x7684;&#x8BDD;&#xFF0C;&#x90A3;&#x4E48;&#x5C31;&#x4F1A;&#x521B;&#x5EFA;/&#x63D2;&#x5165;&#x4E00;&#x4E2A;&#x65B0;&#x7684;&#x6761;&#x76EE;&#x3002;</p>
<pre><code class="lang-go"><span class="hljs-keyword">func</span> (memo *Memo) server(f Func) {
    cache := <span class="hljs-built_in">make</span>(<span class="hljs-keyword">map</span>[<span class="hljs-keyword">string</span>]*entry)
    <span class="hljs-keyword">for</span> req := <span class="hljs-keyword">range</span> memo.requests {
        e := cache[req.key]
        <span class="hljs-keyword">if</span> e == <span class="hljs-literal">nil</span> {
            <span class="hljs-comment">// This is the first request for this key.</span>
            e = &amp;entry{ready: <span class="hljs-built_in">make</span>(<span class="hljs-keyword">chan</span> <span class="hljs-keyword">struct</span>{})}
            cache[req.key] = e
            <span class="hljs-keyword">go</span> e.call(f, req.key) <span class="hljs-comment">// call f(key)</span>
        }
        <span class="hljs-keyword">go</span> e.deliver(req.response)
    }
}

<span class="hljs-keyword">func</span> (e *entry) call(f Func, key <span class="hljs-keyword">string</span>) {
    <span class="hljs-comment">// Evaluate the function.</span>
    e.res.value, e.res.err = f(key)
    <span class="hljs-comment">// Broadcast the ready condition.</span>
    <span class="hljs-built_in">close</span>(e.ready)
}

<span class="hljs-keyword">func</span> (e *entry) deliver(response <span class="hljs-keyword">chan</span>&lt;- result) {
    <span class="hljs-comment">// Wait for the ready condition.</span>
    &lt;-e.ready
    <span class="hljs-comment">// Send the result to the client.</span>
    response &lt;- e.res
}
</code></pre>
<p>&#x548C;&#x57FA;&#x4E8E;&#x4E92;&#x65A5;&#x91CF;&#x7684;&#x7248;&#x672C;&#x7C7B;&#x4F3C;&#xFF0C;&#x7B2C;&#x4E00;&#x4E2A;&#x5BF9;&#x67D0;&#x4E2A;key&#x7684;&#x8BF7;&#x6C42;&#x9700;&#x8981;&#x8D1F;&#x8D23;&#x53BB;&#x8C03;&#x7528;&#x51FD;&#x6570;f&#x5E76;&#x4F20;&#x5165;&#x8FD9;&#x4E2A;key&#xFF0C;&#x5C06;&#x7ED3;&#x679C;&#x5B58;&#x5728;&#x6761;&#x76EE;&#x91CC;&#xFF0C;&#x5E76;&#x5173;&#x95ED;ready channel&#x6765;&#x5E7F;&#x64AD;&#x6761;&#x76EE;&#x7684;ready&#x6D88;&#x606F;&#x3002;&#x4F7F;&#x7528;<code>(*entry).call</code>&#x6765;&#x5B8C;&#x6210;&#x4E0A;&#x8FF0;&#x5DE5;&#x4F5C;&#x3002;</p>
<p>&#x7D27;&#x63A5;&#x7740;&#x5BF9;&#x540C;&#x4E00;&#x4E2A;key&#x7684;&#x8BF7;&#x6C42;&#x4F1A;&#x53D1;&#x73B0;map&#x4E2D;&#x5DF2;&#x7ECF;&#x6709;&#x4E86;&#x5B58;&#x5728;&#x7684;&#x6761;&#x76EE;&#xFF0C;&#x7136;&#x540E;&#x4F1A;&#x7B49;&#x5F85;&#x7ED3;&#x679C;&#x53D8;&#x4E3A;ready&#xFF0C;&#x5E76;&#x5C06;&#x7ED3;&#x679C;&#x4ECE;response&#x53D1;&#x9001;&#x7ED9;&#x5BA2;&#x6237;&#x7AEF;&#x7684;goroutien&#x3002;&#x4E0A;&#x8FF0;&#x5DE5;&#x4F5C;&#x662F;&#x7528;<code>(*entry).deliver</code>&#x6765;&#x5B8C;&#x6210;&#x7684;&#x3002;&#x5BF9;call&#x548C;deliver&#x65B9;&#x6CD5;&#x7684;&#x8C03;&#x7528;&#x5FC5;&#x987B;&#x8BA9;&#x5B83;&#x4EEC;&#x5728;&#x81EA;&#x5DF1;&#x7684;goroutine&#x4E2D;&#x8FDB;&#x884C;&#x4EE5;&#x786E;&#x4FDD;monitor goroutines&#x4E0D;&#x4F1A;&#x56E0;&#x6B64;&#x800C;&#x88AB;&#x963B;&#x585E;&#x4F4F;&#x800C;&#x6CA1;&#x6CD5;&#x5904;&#x7406;&#x65B0;&#x7684;&#x8BF7;&#x6C42;&#x3002;</p>
<p>&#x8FD9;&#x4E2A;&#x4F8B;&#x5B50;&#x8BF4;&#x660E;&#x6211;&#x4EEC;&#x65E0;&#x8BBA;&#x7528;&#x4E0A;&#x9501;&#xFF0C;&#x8FD8;&#x662F;&#x901A;&#x4FE1;&#x6765;&#x5EFA;&#x7ACB;&#x5E76;&#x53D1;&#x7A0B;&#x5E8F;&#x90FD;&#x662F;&#x53EF;&#x884C;&#x7684;&#x3002;</p>
<p>&#x4E0A;&#x9762;&#x7684;&#x4E24;&#x79CD;&#x65B9;&#x6848;&#x5E76;&#x4E0D;&#x597D;&#x8BF4;&#x7279;&#x5B9A;&#x60C5;&#x5883;&#x4E0B;&#x54EA;&#x79CD;&#x66F4;&#x597D;&#xFF0C;&#x4E0D;&#x8FC7;&#x4E86;&#x89E3;&#x4ED6;&#x4EEC;&#x8FD8;&#x662F;&#x6709;&#x4EF7;&#x503C;&#x7684;&#x3002;&#x6709;&#x65F6;&#x5019;&#x4ECE;&#x4E00;&#x79CD;&#x65B9;&#x5F0F;&#x5207;&#x6362;&#x5230;&#x53E6;&#x4E00;&#x79CD;&#x53EF;&#x4EE5;&#x4F7F;&#x4F60;&#x7684;&#x4EE3;&#x7801;&#x66F4;&#x4E3A;&#x7B80;&#x6D01;&#x3002;&#xFF08;&#x8BD1;&#x6CE8;&#xFF1A;&#x4E0D;&#x662F;&#x8BF4;&#x597D;&#x7684;golang&#x63A8;&#x5D07;&#x901A;&#x4FE1;&#x5E76;&#x53D1;&#x4E48;&#x3002;&#xFF09;</p>
<p><strong>&#x7EC3;&#x4E60; 9.3&#xFF1A;</strong> &#x6269;&#x5C55;Func&#x7C7B;&#x578B;&#x548C;<code>(*Memo).Get</code>&#x65B9;&#x6CD5;&#xFF0C;&#x652F;&#x6301;&#x8C03;&#x7528;&#x65B9;&#x63D0;&#x4F9B;&#x4E00;&#x4E2A;&#x53EF;&#x9009;&#x7684;done channel&#xFF0C;&#x4F7F;&#x5176;&#x5177;&#x5907;&#x901A;&#x8FC7;&#x8BE5;channel&#x6765;&#x53D6;&#x6D88;&#x6574;&#x4E2A;&#x64CD;&#x4F5C;&#x7684;&#x80FD;&#x529B;&#xFF08;&#xA7;8.9&#xFF09;&#x3002;&#x4E00;&#x4E2A;&#x88AB;&#x53D6;&#x6D88;&#x4E86;&#x7684;Func&#x7684;&#x8C03;&#x7528;&#x7ED3;&#x679C;&#x4E0D;&#x5E94;&#x8BE5;&#x88AB;&#x7F13;&#x5B58;&#x3002;</p>

                                
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